CORBTOULA FLUMINALIS.. 41 



their Pleistocene series, possibly older than the great ice-sheets of the East of 

 England.^ 



Prof. Boyd Dawkins similarly considers that the deposits of Crayford, Erith, 

 and Grays Thurrock in the Thames valley in which this species occurs, are older 

 than the ice-sheets, a view which M. Rutot accepts as far as Erith is concerned. 

 Prof. Dawkins states that E. print'ig&uius is more abundant at Erith and Crayford, 

 E. antupius being comparatively rare, while at G-rays Thurrock E. anfirpms is the 

 most common.^ 



Referring to Kelsey Hill it is clear that the Gorhicula beds of that locality 

 represent the stage in the Pleistocene epoch in which the greater ice-sheets were 

 disappearing; they have been shown to rest on the basement boulder-clay of 

 Holderness, but they are overlain by a later glacial deposit, the Hessle-clay of 

 S. V. Wood, Jun. 



Gorbicula Jluminalis occurs in the marine gravels of Chatteris and March, to the 

 north of Cambridge, at which places I found, many years ago, a number of specimens 

 together with a molluscan fauna of a Recent but somewhat boreal character, 

 containing a few northern species like Asta7-te horealis, Tellina calcarea and Beld 

 pyramldalis. These gravels rest on the chalky boulder-clay, and are, therefore, 

 like those of Kelsey Hill, later Pleistocene. Lyell also found 0. fluminalis in 

 association with marine shells (probably estuarine) at Menchecourt, near 

 Abbeville.* 



Such facts indicate that the mollusc in question, which had established itself in 

 northern Europe even in Pliocene times, was able to endure the rigorous climate 

 of the Ice Age, flovirishing vigorously in Great Britain when such conditions were 

 passing away. Its subsequent extinction over such an extended area is not easily 

 explained, but it points, I think, to a considerable antiquity for deposits of 

 Pleistocene age like the March gravels, lending no support to the view that in the 

 Eastern Hemisphere at least, the period separating the Great Ice Age from our 

 own was otherwise than prolonged. 



Mr. Kennard seems inclined to consider that the English Gorbicula differs from 

 the typical G. fluminalis, but M. Dollfus, who has made a special study of the 

 subject, says that although this species is undoubtedly variable, he cannot find any 

 material difference between the Recent and the fossil forms ; similar varieties occur 

 in each. In the paper above referred to, the latter writer figures twenty-seven 

 specimens from the Pleistocene beds of Belgium, France and England. Comparing 



1 M. Rutot considers that the presence of Elephas antiquus on the one hand, and of E. primigenius 

 on the other, represent distinct stages in the Pleistocene period, the first of course being the older. 

 This view, however, is not accepted by Prof. Boyd Dawkins. In England, at least, both forms 

 occur together in places ; they may possibly overlap in this country, one having a northern, the other 

 a southern range. 



2 Quart. Journ. G-eol. Soc, vol. xxiii, p. 102, 1867. 



3 Antiquity of Man, ed. 1, p. 124, 1863. 



6 



